1. Field of the Invention
The present invention relates to an ignition apparatus with a pre-gap for automobile engines and the like.
2. Description of the Prior Art
There has been known a pre-gapped ignition apparatus for automobile engines and the like which has a pre-gap connected in series with an ignition plug that has a discharge gap, in order to prevent the ignition plug from smoldering due to adhering carbons and thereby keep the ignition timing constant (Japanese Patent Publication No. Showa 51-32180).
FIG. 6 shows such a pre-gapped ignition apparatus 1. An ignition coil 2 generates a high voltage on the secondary coil side by interrupting a primary coil current. The high voltage thus produced is supplied through a distributor 3 to cylinders in synchronism with the compression stroke of each cylinder in the engine. Each cylinder is provided with a pre-gap 6 which is connected in series with a discharge gap 5 formed between a center electrode and a ground electrode of the ignition plug 4. The pre-gap 6 is installed inside the ignition plug 4.
As shown in FIG. 7, the ignition plug 4 has the center electrode 7 and the ground electrode 8 at one end and, at the other end, a terminal 9 which is connected to a plug cap formed at the end of a high-voltage cable extending from the distributor 3. An insulator 10 of the ignition plug 4 is formed with a center hole 11 extending therethrough from the center electrode 7 to the terminal 9. The pre-gap 6 is placed in the center hole 11 in such a way as to connect the center electrode 7 and the terminal 9. The pre-gap 6 is made up of a pair of discharge electrodes 12, 13 sealed in a glass tube 14 filled with an inert gas at a specified pressure.
In the ignition apparatus 1, the pre-gap 6 is inserted immediately before and in series with the discharge gap 5 of the ignition plug 4, so that a high discharge voltage of the pre-gap 6 is applied to the center electrode 7 of the ignition plug 4, thus providing a required ignition voltage high enough to effect normal firing without being affected by carbon adhering to the ignition plug 4.